EFFECTS OF METHYLPHENIDATE ON SPATIAL WORKING-MEMORY AND PLANNING IN HEALTHY-YOUNG ADULTS

Previous studies of the effects of the psychomotor stimulant, methylph enidate, have concentrated on vigilance and reaction time tasks. In th is study, the effects of methylphenidate on more complex aspects of co gnition were studied using tasks from the CANTAB battery and related t ests which have been shown to be sensitive to frontal lobe dysfunction . Twenty-eight young healthy men participated in a counterbalanced, do uble-blind, placebo-controlled study of the effects of methylphenidate . Cognitive assessment included tests of spatial working memory, plann ing, verbal fluency, attentional set-shifting and sustained attention. Methylphenidate had significant effects on performance of the tests o f spatial working memory and planning but not on the attentional and f luency tests. When the drug was taken on the first test session, perfo rmance on the spatial tests was enhanced by the drug compared to place bo. However, when the drug was taken second, performance accuracy was impaired whereas response latencies were decreased. These results are consistent with a hypothesis that methylphenidate influences performan ce in two conflicting ways; enhancing executive aspects of spatial fun ction on novel tasks but impairing previously established performance. This pattern of effects is discussed within the framework of dual, in teracting arousal mechanisms.